Study On Soil Nutrient And Water Use Efficiency Characteristics Of Zanthoxylum Planispinum Var. Dintanensis In Typical Karst Rocky Desertification Areas Of Guizhou Province

The problem of stone desertification in karst areas was the crux that restricts its regional economic development,social harmony and ecological goodness,and improving the vegetation cover was a crucial part of the process of stone desertification management.There was a direct relationship between vegetation soil and water conservation capacity and the improvement of vegetation cover.Therefore,this study took Zanthoxylum planispinum var.dintanensis in karst stone desertification management demonstration area as the research object to investigate the relationship between water utilization,leaf photosynthetic efficiency and plant growth of Zanthoxylum planispinum var.dintanensis,to reveal the seasonal change pattern of water utilization of Zanthoxylum planispinum var.dintanensis,and to analyze the influencing factors of its water utilization efficiency.It provided scientific basis for the water utilization of Zanthoxylum planispinum var.dintanensis forest,maintenance of ecosystem stability and consolidation of stone desertification management achievements.The main research results obtained in this thesis were as follows:（1）With the change of seasons,the soil bulk weight of Zanthoxylum planispinum var.dintanensis forest showed a trend of first increasing,then decreasing and then increasing;the soil capillary porosity showed a trend of first decreasing and then increasing;the soil water content showed a trend of first increasing and then decreasing;the soil organic carbon showed a trend of first decreasing and then increasing;the root water content and branch water content of Zanthoxylum planispinum var.dintanensis showed a trend of first decreasing and then increasing,and both had the lowest water content in summer.The bulk density and capillary porosity of soil reached the maximum in the flourishing period with the change of growth years.Soil organic carbon showed a trend of increasing,then decreasing and then increasing with the change of growing years.The changes in soil physical and chemical properties and water content of each plant organ were mainly influenced by season and plant growth condition.（2）The percentage of carbon content of each organ of Zanthoxylum planispinum var.dintanensis showed branch>leaf>root in spring and summer,and leaf>branch>root in autumn and winter.From spring to winter,the nitrogen content of each organ of Zanthoxylum planispinum var.dintanensis showed a trend of decreasing and then increasing with the increase of growth years,and the lowest value was found in summer.With seasonal changes,the nitrogen content of each organ showed the pattern of leaf>root>branch>soil.The nitrogen content of Zanthoxylum planispinum var.dintanensis was more influenced by the season,while the carbon content was less influenced by the season.The distribution and transport pattern of water and nutrients of each organ of Zanthoxylum planispinum var.dintanensis was subject to the combined effect of the functional characteristics of its own organs,growth conditions and seasonal changes.Soil water nutrients were closely related to interplant biomass allocation.（3）With seasonal changes,the photosynthetic rate of Zanthoxylum planispinum var.dintanensis showed a trend of increasing then decreasing,leaf transpiration rate was significantly higher in spring than in other seasons.Stomatal conductance was the lowest,and intercellular CO₂concentration were the highest in summer at all growth years of Zanthoxylum planispinum var.dintanensis.Instantaneous water use efficiency of Zanthoxylum planispinum var.dintanensis showed a trend of increasing then decreasing in spring,summer and autumn.Instantaneous water use efficiency of Zanthoxylum planispinum var.dintanensis showed a continuous decrease in winter.With the increase of growth years,photosynthetic rate of 5-year-old Zanthoxylum planispinum var.dintanensis was maximum in autumn and maximum in summer in other growth years.Transpiration rate showed a trend of increasing,then decreasing and then increasing in spring and winter,and was decreasing and then increasing in summer and autumn.The stomatal conductance of 5-and 15-year-old Zanthoxylum planispinum var.dintanensis showed a trend of decreasing and then decreasing,while that of 10-and 20-year-old Zanthoxylum planispinum var.dintanensis showed a trend of decreasing and then increasing.The intercellular CO₂concentration of 5-and 10-year-old Zanthoxylum planispinum var.dintanensis showed a trend of increasing and then decreasing,while that of 15-and 20-year-old Zanthoxylum planispinum var.dintanensis showed a trend of increasing and then decreasing.The instantaneous water use efficiency of 5-and 20-year-old Zanthoxylum planispinum var.dintanensis was lower than that of 10-and 15-year-old Zanthoxylum planispinum var.dintanensis.The stomatal factor was the main factor for the variation of water use efficiency,and the changes of external environmental factors such as season and growth years affected the instantaneous water use efficiency of leaves.（4）With seasonal changes,the stable carbon isotopes and short-term water use efficiency of Zanthoxylum planispinum var.dintanensis showed higher contents in autumn and winter than in spring and summer.The highest stable carbon isotopes were found in spring for 5-year-old Zanthoxylum planispinum var.dintanensis and in summer,autumn and winter for 10-year-old Zanthoxylum planispinum var.dintanensis.With the increase of growing age,the stable carbon isotope content and the short-term water use efficiency of Zanthoxylum planispinum var.dintanensis showed higher in 10 and 15 years of age than in 5 and 20years of age.Soil water content,photosynthetic parameters and stable carbon isotope were the main factors affecting short-term water use efficiency,and the variation of water use efficiency was the result of the combined action of soil and external environmental factors.The instantaneous water use efficiency and short-term water use efficiency in spring,summer and autumn showed a consistent pattern of change.In winter the instantaneous water use efficiency decreased with the increase of growing years,and the short-term water use efficiency showed a change rule of first increasing and then decreasing.The short-term water use efficiency was highest at 15 years in all seasons with the change of growth years,while the instantaneous water use efficiency was different.The maximum value of instantaneous water use efficiency was 15 years old in spring and autumn,and at 10 years in summer,and at5 years in winter.The instantaneous water use efficiency and short-term water use efficiency of 20-year-old tops were always the lowest.